1. Field of the Invention
This invention relates to the art of roofing construction and more particularly to a composite panel for use as a substrate for torch-down roofing membranes and to a roofing construction incorporating such panels.
2. The Prior Art
It has been well known and widely practiced to construct a built-up flat or low-pitched roof by covering the roof deck with alternating layers of felt sheets and molten asphalt. When desired, the deck may first be covered by a substrate of panels known as insulation boards or recovery boards. Such boards, which are frequently made of compressed mats of fibers, are used for thermal insulation of the roof or to provide a uniform surface, particularly when recovering an existing roof. Courses of the boards are secured to the roof deck by nails or other suitable fasteners. Hot, molten asphalt is mopped over the boards, then sheets of roofing felt are rolled out over the asphalt. More asphalt and sheets of felt are applied until the desired thickness is attained.
More recently, the layers of molten asphalt and felt have been replaced by a single ply of a modified bitumen membrane. Such membranes are made of a fabric core carrying a bitumen modified with materials such as fillers, elastomers, surfactants and plasticizers to obtain desired properties. Sheets of the membrane are rolled out over the roofing substrate and are bonded thereto and to adjacent membrane sheets by the direct application of flame from torches or burners.
When, as is frequently the case, the roofing substrate is made of combustible fibers, foams, or other materials, there is the danger of charring, decomposition or even ignition, of the substrate during the torching of the membrane. Accordingly, manufacturers of modified bitumen manufacturers recommend that a noncombustible base sheet be applied over all type of insulation or recovery boards. This is accomplished in the field by rolling out base sheets on the boards and fastening the base sheets to the boards, usually by nailing. The installation of base sheets involves additional costly field labor in the handling, laying down, and fastening of the sheets, and may be especially difficult in windy conditions.